1. Field of the Invention
The present invention relates to a piezoelectric actuator in which a piezoelectric element is used.
2. Description of the Related Art
In a small-diameter observation device such as an endoscope, a piezoelectric actuator using a piezoelectric element is used sometimes as an actuator which bends and vibrates an optical fiber when light scanning is performed by using a light transmitting fiber. As the actuator which bends and vibrates the optical fiber, there is an actuator disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2009-212519.
In this piezoelectric actuator, on an outer peripheral surface of a cylindrical piezoelectric element, an external surface electrode is divided into four electrodes in a peripheral direction so that the electrodes extend in a longitudinal direction (a central axis direction of the cylinder), respectively. In consequence, the four polarized external surface electrodes are formed. Furthermore, an inner peripheral surface of a through hole provided in the center of the cylindrical piezoelectric element is provided with an internal surface electrode which becomes a GND.
At the polarization of the piezoelectric actuator, a direct-current voltage is applied between the external surface electrode and the GND to form the polarization. At an operation of the piezoelectric actuator, an alternating voltage is applied between a pair of external surface electrodes in an X-direction and the GND, whereby one piezoelectric element becomes an elongating region, and the other piezoelectric element becomes a contracting region to generate reverse strain. In consequence, the piezoelectric elements perform a bending resonant vibration in the X-direction. Similarly, the alternating voltage is applied between a pair of external surface electrodes in a Y-direction and the GND, whereby the piezoelectric elements perform the bending resonant vibration in the Y-direction. As a result, the optical fiber can be bent and vibrated in the X-direction and the Y-direction, and the light scanning can be performed in the X-direction and the Y-direction.
In a piezoelectric actuator disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2009-212519, a small-diameter cylindrical body is used in which an outer diameter of a cylindrical piezoelectric element is, for example, about 1 mm or less. However, it is difficult that an external surface electrode is divided into four electrodes in a peripheral direction on an outer peripheral surface of the small-diameter cylindrical body to form the four electrodes thereon, and this operation is noticeably laborious. Moreover, an inner diameter of the cylindrical piezoelectric element is, for example, about 50 μm to 500 μm. Therefore, when an internal surface electrode is provided on an inner peripheral surface of a through hole of the cylindrical piezoelectric element, it is difficult to allow a plating liquid to flow into a cylinder of the small-diameter cylindrical body, which makes it difficult to form the internal surface electrode in the cylinder of the small-diameter cylindrical body by plating, and this operation is similarly noticeably laborious.